Charcoal Kiln V.4.0

As part of the island kajiba project, reclaimed and natural materials were used to construct a larger traditional style charcoal making kiln. The basic concept is a simple chamber with a door on one end and a chimney on the other, insulated and sealed by being buried in clay/soil, and roofed to keep off the rain.

After more than six years of successful forging with charcoal made in the Charcoal Kiln V.3, the kajiba project afforded the opportunity to create a more permanent kiln for making charcoal. The Iwasaki kiln, a scaled down and modified version of a traditional Japanese charcoal making kiln, is relatively easy to build, load, tend, is long lasting, makes consistent charcoal batches, and is still my first recommendation for those wishing to begin learning to make charcoal for blacksmithing and bladesmithing.

Other than size, the main difference between the Iwasaki~san’s design and this traditional style charcoal kiln is that there is no separation between the combustion chamber and the pyrolization chamber other than the fuel materials and kiln loading itself. Materials used in this project were mainly earth, stones, reclaimed wood, and scrap steel that was on hand.


Laying the Foundation

Building a Charcoal Making Kiln
A stone bed/pit under the chimney with a buried pipe to drain excess water as it condenses.
Building a Charcoal Making Kiln
The base of the chimney is a large chamber to prevent clogging due to build up of condensed tar.
Building a Charcoal Making Kiln
The drain pipe and the base for the chimney, plenty of scrap used in this project.
Building a Charcoal Making Kiln
Reclaimed roofing provides a bit of a vapor barrier from the ground, the kiln will be raised off of it by a few centimetres to help heat retention.

Fabricating the Interior

Building a Charcoal Making Kiln
The location of the chimney, in this case a six inch diameter steel pipe from an early retort experiment.
Building a Charcoal Making Kiln
The opening to the chimney chamber, pulling from the bottom rear of the charcoal chamber.
Building a Charcoal Making Kiln
A colourful visitor to the kiln during construction.
Building a Charcoal Making Kiln
The floor slopes slightly down toward the back of the kiln to move the coolest air toward the chimney.
Building a Charcoal Making Kiln
A piece of heavy corrugated steel roof provides some space for draft along the floor and adds strength.
Building a Charcoal Making Kiln
The remainder of the piece provides insulation and strength across the top of the kiln.
Building a Charcoal Making Kiln
A view into the kiln, the door is fairly large but will make loading and unloading easier.

Building the Frame

Building a Charcoal Making Kiln
The frame will serve to support the roof as well as contain the soil that insulates the kiln.
Building a Charcoal Making Kiln
The tapered shape of the kiln is visible, moving the rising heat towards the back of the kiln.
Building a Charcoal Making Kiln
Three layers of reclaimed sheet roofing are used to contain and insulate the soil.
Building a Charcoal Making Kiln
Repurposed roof peak covers the open ends of the roof corrugation and keeps the soil from falling out.
Building a Charcoal Making Kiln
Stones and sloped soil around the outside to assist drainage away from the kiln.
Building a Charcoal Making Kiln
Ready for filling with a clay/soil mixture, large stones form a working area in front of the door.
Building a Charcoal Making Kiln
The interior of the kiln tapers from about 3’x3′ at the door to 4’x4′ at the back.

Insulating with Soil

Building a Charcoal Making Kiln
The space to be filled around the chimney assembly.
Building a Charcoal Making Kiln
View of the space along one of the sides and some of the stones supporting the kiln.
Building a Charcoal Making Kiln
The narrowest area at the corners will still provide about 8 inches of insulation.
Building a Charcoal Making Kiln
A large volume was required to fill around the chimney.
Building a Charcoal Making Kiln
The structure handling the weight of the soil well, once the moisture comes out it will be lighter.
Building a Charcoal Making Kiln
The chimney will sit flush with the surface as it will need to be sealed with soil after each firing.
Building a Charcoal Making Kiln
Ready to build the roof before the rains come.

Roof and Finishing Details

Building a Charcoal Making Kiln
Building the roof using available scrap wood.
Building a Charcoal Making Kiln
Finishing the front of the kiln with stones and backfilling with soil.
Building a Charcoal Making Kiln
The door is currently made of stacked stones, all of the gaps will need to be sealed with clay/soil mud during operation to control airflow.
Building a Charcoal Making Kiln
Heavy steel protects the roof from the heat of the chimney, brackets and shelves for storage.
Building a Charcoal Making Kiln
More brackets for storage on the rear wall.
Building a Charcoal Making Kiln
The stone paved work area in front of the kiln is partially protected by the roof overhang and will be used for splitting wood as well as unloading and sorting charcoal.
Building a Charcoal Making Kiln
View of the kiln with the kajiba, see the whole building project here.
Building a Charcoal Making Kiln
Slowly drying the soil insulation before winter with a small scrap wood fire in the kiln.

A curated video playlist of making and using traditional charcoal kilns in Japan, the first two videos are for swordsmithing charcoal, followed by other styles mainly for cooking and grilling charcoal:


A kiln construction book in Japanese, with some helpful illustrations and measurements:
炭やき教本 (on amazon.com)
炭やき教本 (on amazon.co.jp)
2019 new edition (on amazon.co.jp)


Read more about the charcoal making process and why we do it: How Charcoal is Made
Read some background information on fuel alternatives: Sustainable ‘Smithing?
Follow the charcoal making progress: All posts tagged Charcoal

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